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Intel® PXA255 Processor Developer’s Manual 16-29
Network SSP Serial Port
As the system accesses the register, FIFO control logic transfers data automatically between the
registers and FIFOs as fast as the system moves it. Unless attempting a write to a full transmit
FIFO, data in the FIFO shifts up or down to accommodate the new word(s). Status bits show users
whether the FIFO is full, above the programmable trigger threshold, below the programmable
trigger threshold or empty.
For transmit data transfers, the register can be written by the system processor anytime it falls
below its trigger threshold when using programmed I/O.
When a data size of less than 32-bits is selected, do not left-justify data written to the transmit
FIFO. Transmit logic left-justifies the data and ignores any unused bits. Received data of less than
32-bits is automatically right-justified in the receive FIFO.
When the SSP is programmed for the Microwire* protocol and the size of the Transmit data is eight
bits (SSCR1[MWDS] cleared), the most significant bits are ignored. Similarly, if the size for the
Transmit data is 16 bits (SSCR1[MWDS] set), the most significant 16 bits are ignored.
SSCR0[DSS] controls the Receive data size.
Both FIFOs are cleared when the port is reset, or by clearing SSCR0[SSE].
This is a read/write register. Ignore reads from reserved bits. Write zeros to reserved bits.
16.6 Network SSP Serial Port Register Summary
Table 16-10 shows the registers associated with the NSSP and their physical addresses.
Table 16-9. SSDR Bit Definitions
0x4140_0010 SSDR Network SSP Serial Port
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
DATA
Reset
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
Bits Name Description
31:0 DATA
TRANSMIT/RECEIVE DATA:
Data word to be written to/read from Transmit/receive FIFO
Table 16-10. NSSP Register Address Map
Physical Address Name Description
0x4140_0000 NSSCR0 NSSP Control register 0
0x4140_0004 NSSCR1 NSSP Control register 1
0x4140_0008 NSSSR NSSP Status register
0x4140_000C NSSITR NSSP Interrupt Test register
0x4140_0010 NSSDR NSSP Data Write Register / Data Read register
0x4140_0028 NSSTO NSSP Time Out register
0x4140_002C NSSPSP NSSP Programmable Serial Protocol